Olefins, also commonly known as alkenes, are important items of commerce. Their many applications include employment as intermediates in the manufacture of detergents, as precursors to more environmentally-friendly refined oils, as monomers, and as precursors for many other types of products. An important subset of olefins are alpha olefins, and one process of making alpha olefins is via oligomerization of ethylene, which is a catalytic reaction involving various types of catalysts and/or catalyst systems. Examples of catalysts and catalyst systems used commercially to produce alpha olefins include alkylaluminum compounds, certain nickel-phosphine complexes, titanium halides with a Lewis acid (e.g., diethyl aluminum chloride), zirconium halides and/or zirconium alkoxides with alkylaluminum compounds. Additionally, there is a selective ethylene trimerization and/or tetramerization catalyst system for producing 1-hexene that uses a chromium containing compound (e.g., a chromium carboxylate), a nitrogen-containing ligand (e.g., a pyrrole), and a metal alkyl (e.g., alkyl aluminum compounds).
Several non-commercial oligomerization catalyst systems to produce alpha olefins are based upon metal complexes of pyridine bis-imines, metal complexes of α-diimine compounds having a metal complexing group, and selective trimerization and/or tetramerization catalyst systems using a metal compound (e.g., a chromium compound) complex of a diphosphinylamine, phosphinyl formamidine, phosphinyl amidine, or phosphinyl guanidine. These catalyst systems typically use an organoaluminum compound (e.g., aluminoxane) as a component of the catalyst systems for olefin oligomerization.
Applications and demand for olefins (e.g., alpha olefins) continue to multiply, and competition to supply them correspondingly intensifies. Thus, additional novel and improved catalyst systems and processes for olefin oligomerization are desirable.